<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        ul {
            list-style: none;
            padding: 0;
            margin: 0;
        }

        body {
            background: #23384e;
            font: 12px/1.5 \5fae\8f6f\96c5\9ed1;
        }

        .search,
        .search .inner-box,
        .search .box,
        .search .select,
        .search a {
            background: url(images/search.jpg) no-repeat;
        }

        .search,
        .search .box,
        .search .inner-box {
            height: 34px;
        }

        .search {
            position: relative;
            width: 350px;
            margin: 10px auto;
        }

        .search .box {
            background-position: right 0;
        }

        .search .inner-box {
            background-repeat: repeat-x;
            background-position: 0 -34px;
            margin: 0 20px 0 40px;
        }

        .search .select {
            float: left;
            color: #fff;
            width: 190px;
            height: 22px;
            border: none;
            cursor: pointer;
            margin-top: 4px;
            line-height: 22px;
            padding-left: 10px;
            background-position: 0 -68px;
        }

        .search a {
            float: left;
            width: 80px;
            height: 24px;
            color: #333;
            letter-spacing: 4px;
            line-height: 22px;
            text-align: center;
            text-decoration: none;
            background-position: 0 -90px;
            margin: 4px 0 0 10px;
        }

        .search a:hover {
            color: #f60;
            background-position: -80px -90px;
        }

        .search ul {
            position: absolute;
            top: 26px;
            left: 40px;
            color: #fff;
            width: 198px;
            background: #2b2b2b;
            border: 1px solid #fff;
            display: none;
        }

        .search ul li {
            height: 25px;
            line-height: 24px;
            cursor: pointer;
            padding-left: 10px;
            margin-bottom: -1px;
            border-bottom: 1px dotted #fff;
        }

        .search ul li:hover,
        .search ul li.active {
            background: #8b8b8b;
        }
    </style>
</head>

<body>
    <div class="search">
        <div class="box">
            <div class="inner-box">
                <input type="text" id="keyword" class="select" autocomplete="off" placeholder="请选择游戏名称">
                <a href="#">搜索</a>
            </div>
        </div>
        <ul class="list">
            <li>地下城与勇士</li>
            <li>魔兽世界（国服）</li>
            <li>魔兽世界（台服）</li>
            <li>热血江湖</li>
            <li>大话西游II</li>
            <li>QQ幻想世界</li>
        </ul>
    </div>
</body>

</html>
<script>
    /*
            实现的功能：
                【1】搜索框获取焦点的时候 显示下拉下单
                    【1】获取元素
                【2】搜索框失去焦点时候 隐藏下拉菜单

                一下两个功能只有在获取焦点的时候才会有用
                【3】按下鼠标的上下键 可以动态选中 li元素（给li元素添加 active 这个class名）
                【4】当按下 enter键的时候，把拥有 activeclass名的元素的内容 赋值给搜索框
         */
    var keyword = document.querySelector('#keyword');
    var list = document.querySelector('.list');
    var lists = document.querySelectorAll('.list>li');
    var index = -1;
    //绑定焦点事件
    keyword.onclick = function (event) {
        list.style.display = 'block'
        document.onkeydown = function (e) {
            //上键
            if (e.keyCode === 40) {
                index++;
                if (index > lists.length - 1) {
                    index = 0;
                }
                for (var i = 0; i < lists.length; i++) {
                    lists[i].className = '';
                }
                lists[index].className = "active"
            }
            //下键
            if (e.keyCode === 38) {
                index--;
                if (index < 0) {
                    index = lists.length - 1;
                }
                // 排他思想
                for (var i = 0; i < lists.length; i++) {
                    lists[i].className = '';
                }
                lists[index].className = 'active';
            }
            //确定键
            if (e.keyCode === 13) {

                keyword.value = lists[index].innerHTML;
                list.style.display = 'none';
                keyword.blur();
            }
        }
        //点击
        lists.forEach(function (items, index) {
            items.onclick = function () {
                for (var i = 0; i < lists.length; i++) {
                    lists[i].className = '';
                }
                lists[index].className = 'active';
                keyword.value = this.innerHTML;
            }
        })
        //阻止事件传播
        if (e && e.stopPropagation) { //非IE 
            e.stopPropagation();
        } else { //IE 
            window.event.cancelBubble = true;
        }
        //失去焦点，菜单隐藏
        document.onclick = function () {
            list.style.display = 'none';
        }

    }
</script>